An evaluation of the integration of pharmacokinetic and pharmacodynamic principles in clinical drug development. Experience within Hoffmann La Roche.

The integration of pharmacokinetic and pharmacodynamic principles into drug development has been proposed as a way of making it more rational and efficient. The use of these principles in drug development to make scientific and strategic decisions is defined as the 'pharmacokinetic-pharmacodynamic guided approach to drug development'. The objectives of this survey were: (i) to assess the extent the pharmacokinetic-pharmacodynamic guided approach to drug development has been used in a large multinational pharmaceutical company: (ii) to evaluate the impact of pharmacokinetic and/or pharmacodynamic results on clinical drug development; and (iii) to identify factors which prevented the full application of the pharmacokinetic-pharmacodynamic guided approach. This was done by looking at 18 projects in the current development portfolio at Hoffman La Roche and evaluating the use of this approach by interviewing the responsible clinical pharmacologist using a standardised questionnaire. (i) Benefits from using the pharmacokinetic-pharmacodynamic guided approach were reported in every project, independent of development phase and therapeutic area. This approach was more extensively used in the recent projects. The selection of dosages in clinical studies was found to be the most important application of pharmacokinetic-pharmacodynamic results in terms of an impact on drug development. (ii) Time savings, up to several months, could be quantified in 8 projects during the entry-into-man studies and in 6 projects during the phase II or III studies. In 4 projects, 1 clinical study was avoided. (iii) The most important scientific factor preventing the full application of the approach was the lack of knowledge on the predictive value of the pharmacodynamic or surrogate marker for effect (6 projects). The results of the survey have shown that the use of the pharmacokinetic-pharmacodynamic guided approach has contributed to making clinical drug development more rational and more efficient. Opportunities to apply the pharmacokinetic-pharmacodynamic approach should be identified in each project and a project specific strategy for the pharmacokinetic-pharmacodynamic guided approach should be defined during phase 0 of drug development.

Pharmacokinetics of retinoids in women after meal consumption or vitamin A supplementation.

These studies were conducted to evaluate the pharmacokinetics of several retinoids after meal consumption or vitamin A supplementation to establish a reference for future assessment of teratogenic risks of retinoid therapeutic agents. In the first study, 36 healthy young female volunteers consumed single meals containing vitamin A amounts ranging from 1,305 to 169,474 IU. In the second study, 24 other female volunteers took vitamin A supplements at a dose level of 5,000, 10,000, or 25,000 IU/day for 60 days. Plasma concentrations of tretinoin, isotretinoin, 4-oxo-tretinoin, and 4-oxo-isotretinoin in samples collected during the studies were analyzed using a high-performance liquid chromatography method with ultraviolet detection. Pharmacokinetic parameters for the retinoids were calculated using model-independent methods. Plasma concentrations of tretinoin were not altered by meal consumption or vitamin A supplementation. Plasma levels of 4-oxo-tretinoin were below the assay detection limit (0.3 ng/mL) in the majority of samples collected throughout the studies. Linear relationships between dose and maximum concentration (Cmax) and dose and area under the concentration-time curve (AUC) for isotretinoin and 4-oxo-isotretinoin were derived from data from the meal study. For the most bioavailable formulation used in the supplement study, daily ingestion of 5,000 IU of vitamin A caused increases of 141 +/- 53% and 171 +/- 77% from baseline in the 24-hour AUCs of isotretinoin and 4-oxo-isotretinoin, respectively. Dose-related increases in systemic exposure to retinoids were observed after ingestion of vitamin A by means of a meal or a supplement. Findings from these studies can be used as a basis for future safety evaluations of retinoid compounds.

Effect of the lipase inhibitor orlistat on the pharmacokinetics of four different antihypertensive drugs in healthy volunteers.

OBJECTIVE: To study the influence of the lipase inhibitor orlistat on the pharmacokinetics of the antihypertensive drugs atenolol, furosemide, captopril and nifedipine. METHODS: Four open-label, crossover studies were performed on six to eight healthy male volunteers. Orlistat was given in doses of 50 mg 3 times daily mid-meal for 7 (nifedipine and captopril) or 8 days (atenolol and furosemide). The four antihypertensive drugs (atenolol 100-mg tablet, furosemide 40-mg tablet, captopril 50-mg tablet and nifedipine 20-mg slow-release tablet) were administered in single doses twice, once before and once together, with orlistat at the end of the orlistat treatment period. RESULTS: The plasma concentration time profiles and the pharmacokinetic parameters estimated for these drugs were in the expected range, except for furosemide, whose bioavailability was lower than reported in the literature. This was probably due to the fact that furosemide was given during a meal. There were minor, but statistically significant, differences in one of the pharmacokinetic parameters of furosemide and nifedipine (no difference for captopril and atenolol) when these drugs were given alone and in combination with orlistat: the half-life of furosemide was slightly longer, the time to peak plasma concentrations of nifedipine was slightly longer. None of these are considered to be clinically significant changes. CONCLUSIONS: The lipase inhibitor orlistat given 50 mg 3 times daily does not alter the pharmacokinetics of atenolol, furosemide, nifedipine and captopril to a clinically significant extent.

Multiple-dose clinical pharmacology of the catechol-O-methyl-transferase inhibitor tolcapone in elderly subjects.

OBJECTIVE: The purpose of this study was to assess the multiple-dose clinical pharmacology of tolcapone, a novel catechol-O-methyltransferase (COMT) inhibitor, in elderly subjects. METHODS: The drug was administered orally t.i.d. for 7 days to four sequential groups of eight elderly subjects (gender ratio 1:1) at doses of 100, 200, 400 and 800 mg in a double-blind, randomised, placebo-controlled, ascending-multiple-dose design. On days 2 and 7, a single dose of levodopa/benserazide 100/25 mg was given 1 h after the first intake of tolcapone. Plasma concentrations of tolcapone; its metabolite 3-O-methyltolcapone, levodopa and 3-O-methyldopa were determined during the course of the study in conjunction with COMT activity in erythrocytes. RESULTS: Tolcapone was well tolerated at all dose levels, with a slight increase in gastrointestinal adverse events in females at higher doses. The drug was rapidly absorbed and eliminated and showed no changes in pharmacokinetics with time during multiple doses of 100 and 200 mg t.i.d. At doses of 400 and 800 mg t.i.d., tolcapone accumulated moderately as reflected in increased Cmax and AUC values. Despite the long halflife of 3-O-methyltolcapone (39 h), only minor accumulation occurred due to suppression of its formation by tolcapone. The pharmacodynamics of tolcapone did not change during the week of treatment as reflected in inhibition of COMT activity in erythrocytes, the derived parameters of the plasma concentration-effect relationship (inhibitory Emax model with constant EC50 values) and the effect on levodopa pharmacokinetics (1.6 to 2.5-fold increase in bioavailability). This suggests the absence of tolerance development and the insignificance of the altered pharmacokinetics at 400 and 800 mg t.i.d. with regard to the pharmacodynamics. CONCLUSION: The results of this study offer promising perspectives for the application of tolcapone as adjunct therapy to levodopa in the treatment of Parkinson's disease.

Pharmacokinetic-pharmacodynamic interaction between the COMT inhibitor tolcapone and single-dose levodopa.

1. Single oral doses of the catechol-O-methyltransferase (COMT) inhibitor tolcapone (10-800 mg) or placebo were administered simultaneously with a dose of levodopa/benserazide 100/25 mg to seven sequential groups of six healthy male subjects in a two-way crossover study. 2. Plasma concentrations of tolcapone, its metabolite 3-O-methyltolcapone, levodopa and 3-O-methyldopa (3-OMD) were determined in conjunction with COMT activity in erythrocytes. 3. The drug combination was well tolerated at all dose levels and there were no signs indicative of an increase in dopaminergic stimulation. 4. Tolcapone caused a rapid and reversible inhibition of COMT activity in erythrocytes in parallel with a dose-dependent decrease in the formation of 3-OMD. Tolcapone increased the area under the concentration-time curve and elimination half-life of levodopa. The maximum effects were obtained at a dose of about 200 mg when both parameters increased approximately twofold. The drug had no influence on the maximum concentration of levodopa. 5. Tolcapone was rapidly absorbed and eliminated with, on average, a tmax of 1.5 h and a t1/2 of 2.3 h. The drug showed dose-proportional pharmacokinetics, in contrast to 3-O-methyltolcapone whose formation was relatively decreased at higher doses. 6. Plasma concentrations of tolcapone correlated with inhibition of COMT activity in erythrocytes and suppression of 3-OMD levels, but not with changes in levodopa pharmacokinetics.

Pharmacokinetics and pharmacodynamics of Ro 41-3696, a novel nonbenzodiazepine hypnotic.

This report describes the first evaluation in humans of Ro 41-3696. Based on its preclinical profile, Ro 41-3696, a nonbenzodiazepine partial agonist at the benzodiazepine receptor, offers promising perspectives as an innovative hypnotic drug in that it does not exhibit most of the disadvantages associated with full agonists. Single oral doses of 0.1, 0.3, 1.0, 3.0, 10, and 30 mg were administered sequentially to six groups of six healthy male volunteers in a placebo-controlled, double-blind design. Tolerability was assessed and pharmacokinetic and pharmacodynamic measurements were conducted during a period of 28 hours after drug intake. Ro 41-3696 was well tolerated at all doses, causing no clinically relevant changes in vital signs or laboratory parameters. At doses of 10 and 30 mg there were signs of unsteady gait, indicating a central nervous system depressant effect. Pharmacokinetic analyses revealed that Ro 41-3696 was absorbed and eliminated rapidly (tmax = approximately 1 hour; t1/2 = approximately 4 hours). At all times plasma levels of Ro 41-3290, the desethylated derivative of Ro 41-3696, were higher than those of the parent drug (tmax and t1/2 values = approximately 2 and 8 hours, respectively). Area under the curve (AUC) data indicated dose-proportional pharmacokinetics for both Ro 41-3696 and Ro 41-3290. Performance in both a tracking and a memory search test was significantly affected by doses of 10 and 30 mg, and long-term memory, as assessed by a word learning and recall test, was slightly impaired at these doses. The results of this study support the initiation of therapeutic efficacy studies with Ro 41-3696 in doses up to approximately 5 mg and further exploration of the characteristics of Ro 41-3290.

Integrated pharmacokinetics and pharmacodynamics of the novel catechol-O-methyltransferase inhibitor tolcapone during first administration to humans.

OBJECTIVES: To assess the tolerability, pharmacokinetics and pharmacodynamics of single oral doses of the novel catechol-O-methyltransferase (COMT) inhibitor tolcapone in healthy volunteers. METHODS: In this double-blind, placebo-controlled, ascending-single-dose study, doses of 5 to 800 mg tolcapone were administered orally to eight sequential groups of six young healthy male volunteers. Adverse events, vital signs, and clinical laboratory variables were recorded. Pharmacokinetic parameters of tolcapone and its 3-O-methylmetabolite were determined. Pharmacodynamics were assessed by determination of COMT activity in erythrocytes. RESULTS: Tolcapone was well tolerated at all dose levels and did not exert a detectable influence on vital sign measurements. The drug was rapidly absorbed and showed dose-proportional pharmacokinetics. Its mean elimination half-life was 2.0 +/- 0.8 hours (n = 42). Plasma levels of the 3-O-methylmetabolite of tolcapone were not proportional to dose, and its formation was delayed at higher doses. Its elimination half-life was 32 +/- 7 hours (n = 29). Tolcapone caused a rapid and reversible inhibition of COMT activity in erythrocytes. At doses of 200 mg and higher, COMT activity was inhibited by more than 80%. The pharmacokinetic-pharmacodynamic relationship could be described by an inhibitory Emax model and suggested that metabolites of tolcapone did not substantially contribute to its inhibitory activity. CONCLUSIONS: The novel COMT inhibitor tolcapone was well tolerated at oral doses of 5 to 800 mg. Tolcapone concentration-dependently inhibited COMT activity in erythrocytes and exhibited dose-proportional kinetics. Further investigations into its applicability in the treatment of Parkinson's disease are warranted.

Sympathetic activity and presynaptic adrenoceptor function in patients with longstanding essential hypertension.

OBJECTIVE: To assess the contribution of the sympathetic nervous system to the hypertension in patients with longstanding essential hypertension. DESIGN: Overall sympathetic function, presynaptic adrenoceptors and neuronal re-uptake were examined after withdrawal of medication for at least 3 weeks in eight patients with longstanding essential hypertension and in eight carefully matched normotensive control subjects. METHODS: Minimal forearm vascular resistance after 10 min ischaemia was used as a measure of structural vascular changes. Overall sympathetic tone was assessed using tilt testing and pressor dose infusion of noradrenaline. The presence and function of presynaptic adrenoceptors and the neuronal re-uptake of noradrenaline were evaluated in the forearm using tracer noradrenaline kinetics with measurement of forearm noradrenaline plasma appearance rate and noradrenaline plasma spillover. Intra-arterial infusions of tritiated noradrenaline, the endogenous alpha- and beta-adrenoceptor agonist adrenaline, the alpha-adrenoceptor blocker phentolamine, the non-adrenergic vasodilator sodium nitroprusside and the neuronal re-uptake inhibitor desipramine were given in the forearm. RESULTS: We found that the hypertensives had higher minimal forearm vascular resistance, indicating structural vascular changes; decreased overall sympathetic activity, indicated by a lower basal whole-body noradrenaline production rate; enhanced vasopressor sensitivity for exogenously administered noradrenaline with decreased arterial baroreflex sensitivity; indications of decreased forearm neuronal re-uptake; evidence consistent with the presence of presynaptic, release-facilitating beta-adrenoceptors in the forearm, apparently not functionally different between the two groups; and undecisive evidence for the presence of functional presynaptic alpha-adrenoceptors in the forearm. CONCLUSIONS: In patients with longstanding essential hypertension we found decreased overall sympathetic activity, with indications of decreased forearm neuronal re-uptake, which might have a compensatory role. We found indications of structural vascular changes and diminished baroreflex sensitivity in the hypertensives, which contribute to the hypertension. However, peripheral presynaptic, release-facilitating beta-adrenoceptors seem to be present, which are functionally not clearly different between the two groups. Observations on peripheral presynaptic alpha-adrenoceptors were inconclusive.

Multiple dose pharmacokinetics and concentration effect relationship of the orally active renin inhibitor remikiren (Ro 42-5892) in hypertensive patients.

1 Three double-blind, randomized, placebo controlled, multiple oral dose studies in patients with mild to moderate hypertension were performed to study tolerability, pharmacodynamics and pharmacokinetics of remikiren. Doses of 100-800 mg remikiren or placebo were given over 8 days to altogether 144 patient volunteers. In some cases (n = 46) single i.v. doses of 100 mg were administered 4 h after the last oral dose. Plasma remikiren concentrations, plasma renin activity and immunoreactive renin concentrations were measured. Pharmacokinetic parameters were estimated using model independent techniques and the concentration-effect relationship was evaluated using population pharmacometric methods. 2 In most patients no distinct absorption and disposition phase could be identified, since plasma concentrations fluctuated widely over a period of approximately 10 h. Peak plasma concentrations (Cmax) were achieved within 0.25-2 h postdose. Mean Cmax values (on the first and last day of oral treatment) were in the magnitude of 4-6 ng ml(-1) (200 mg), 23-27 ng ml(-1) (300 mg), 65-83 ng ml(-1) (600 mg) and 47-48 ng ml(-1) (800 mg). Cmax and AUC0-t values were clearly different for different doses within single studies. Intersubject variability in pharmacokinetic parameters was much higher than intrasubject variability. No drug accumulation in plasma was apparent. 3 Inhibition of the angiotensin I production rate correlated well with plasma drug concentrations according to the Emax-model. An IC50 value of 0.5 ng ml(-1) (0.8 nM) was estimated. No correlation between blood pressure changes on the last day of oral treatment and either plasma remikiren concentrations or plasma renin inhibition was found.

Comparison of blood pressure and angiotensin responses to the renin inhibitor Ro 42-5892 and the angiotensin converting enzyme inhibitor enalapril in essential hypertension.

OBJECTIVE: To compare the responses of angiotensin II (Ang II) and blood pressure to the renin inhibitor Ro 42-5892 and the angiotensin converting enzyme (ACE) inhibitor enalapril. SUBJECTS: Eight non-sodium-restricted patients with mild-to-moderate essential hypertension. DESIGN: A single-blind crossover study. Ro 42-5892 (600 mg orally, once a day) and enalapril (20 mg orally, once a day) were given for 8 days before detailed investigations were carried out. METHODS: Ambulatory blood pressure was measured directly for 24 h by the Oxford technique on three occasions. Off-treatment and on day 8 of treatment with Ro 42-5892 and with enalapril. Ang II was measured by radioimmunoassay after separation by high-performance liquid chromatography. RESULTS: Plasma renin activity and Ang II were lowered by 83% [95% confidence interval (CI) 61-105] and 68% (95% CI 49-87), respectively, 0.5-1 h after Ro 42-5892, but after only 3 h values had returned to baseline. Unlike this rapid and short-term suppression of Ang II, the maximal antihypertensive response to Ro 42-5892 (fall in blood pressure 12.9/9.0 mmHg) occurred only after 6 h. Blood pressure returned to baseline after 8 h. In response to enalapril, Ang II was maximally suppressed by 63% (95% CI 32-94) after 2 h and by 83% (95% CI 76-90) after 8 h. Despite early maximal Ang II suppression, the maximal antihypertensive response to enalapril occurred only after 12 h (fall in blood pressure 25.3/16.3 mmHg). With this compound a significant antihypertensive effect was still present 24 h after dosing. CONCLUSIONS: Compared with enalapril at 20 mg once a day, repeated oral administration of a single dose of Ro 42-5892 at 600 mg caused only short-term suppression of Ang II and blood pressure. Suppression of Ang II and reduction in blood pressure were temporally dissociated, both with the ACE inhibitor and the renin inhibitor. This implies that the blood pressure lowering effect of these inhibitors is caused partly by Ang II suppression outside the circulation.

Betaxolol in obese hypertensive patients. Long-term effects on blood pressure and serum lipids.

The antihypertensive and metabolic effects of betaxolol (20 mg/day) were monitored in 40 patients (17 male), aged 54 +/- 2 yr (mean +/- SEM), with moderate essential hypertension. In a subgroup, consisting of 35 obese patients with a Quetelet index greater than 25.0, blood pressure, heart rate, side effects and biochemical variables were registered bi-monthly for a period of 6 months and after a placebo run-in and run-out period of 2 weeks. Betaxolol decreased blood pressure from 165 +/- 3/107 +/- 1 to 151 +/- 3/95 +/- 2 mmHg after 2 weeks and further to 151 +/- 3/93 +/- 2 mmHg after 6 months (p less than 0.001). Ninety percent of the patients responded to therapy with betaxolol. Heart rate fell from 77 +/- 2 to 64 +/- 1 bpm (p less than 0.001). No significant changes were observed in levels of total cholesterol, LDL-cholesterol or HDL-cholesterol. Triglycerides tended to increase from 2.2 +/- 0.3 to 2.8 +/- 0.4 mmol/l after 4 months of treatment (NS). Renal function was not influenced by betaxolol. Side effects, recorded on a standard questionnaire, did not differ between betaxolol and placebo. In conclusion, betaxolol in a fixed dose of 20 mg/day is an effective antihypertensive drug in the long-term treatment of obese, hypertensive patients, without adverse effects on lipoproteins.

Serotonergic receptors and drugs in hypertension.

The possible role of 5-hydroxytryptamine (5HT) and 5HT-receptors in hypertension, already suggested by Page in 1954, has been subject to a renaissance of interest owing to the development of antihypertensive drugs which interact with 5HT-receptors. These drugs, like ketanserin, urapidil and flesinoxan are used as tools to study the role of 5HT and its receptors in hypertension. Some arguments would plead in favour of a certain role of 5HT and 5HT-receptors in the pathogenesis and maintenance of hypertension: hyperresponsiveness of blood vessels from hypertensive patients and animals to 5HT-induced constriction; the antihypertensive/vasodilator activity of the 5HT2-receptor antagonist ketanserin; enhanced sensitivity of platelets from hypertensives to 5HT. However, there are also several arguments which do not support a causal role of 5HT in hypertensive disease: 5HT is not a generally accepted pressor agent, whereas its concentration in the circulating blood is subthreshold; the 5HT2-receptor antagonist ketanserin is the only agent of this type which lowers blood pressure, other 5HT2-receptor blockers (ritanserin; LY 53587) being inactive. The various data and arguments available do not unequivocally support a relevant role of peripheral 5HT and its receptors in hypertensive disease. 5HT2-receptor blockade may, however, have a favourable effect on the microcirculation under pathological conditions. The stimulation of central 5HT1A-receptors by drugs like urapidil, 8-OH-DPAT or flesinoxan, has been demonstrated to induce peripheral sympathoinhibition and a fall in blood pressure. This mechanism appears to be a novel target for centrally acting antihypertensives, clearly different from that of clonidine and related drugs, which are centrally acting alpha 2-adrenoceptor agonists.

Functional and structural determinants of glomerulosclerosis in the fawn-hooded rat.

The effect of uninephrectomy (UN) at 4 months of age was studied on several parameters involved in the development of glomerulosclerosis (GS) in male spontaneously hypertensive Fawn-Hooded rats. Protein excretion per animal was significantly more increased in UN rats at 2 months after operation compared to sham operated controls (202 +/- 104 vs. 88 +/- 37 mg 24 h-1, P = 0.005) and remained significantly higher throughout the rest of the observation period. At 11 months of age UN rats had a marked increase in the incidence of GS, 37 +/- 16% compared to 5 +/- 3% (P less than 0.001) in controls. No differences were observed in mean arterial blood pressure. Functional studies in separate groups of rats at 5 months of age showed an increase in single kidney glomerular filtration rate in UN rats (0.40 +/- 0.07 vs. 0.28 +/- 0.09 ml min-1 100 g, P = 0.006). Single kidney renal plasma flow and filtration fraction were not altered. Mean glomerular volume was increased 1 month after UN (1.86 +/- 0.25 vs. 1.39 +/- 0.25 x 10(6) microns 3, P = 0.003). Urinary noradrenaline excretion per animal (24-h) showed a high sympathic nervous tone in both sham and UN rats. Total urinary dopamine and kallikrein excretion per animal were not influenced by UN. These data indicate that after UN the development of GS in this rat strain is accelerated in association with compensatory hyperfiltration and glomerular volume expansion, which may play a role in the pathogenesis of GS.

The effect of a converting enzyme inhibitor upon renal damage in spontaneously hypertensive Fawn Hooded rats.

OBJECTIVE: To determine the effect of angiotensin converting enzyme inhibition (CEI) upon renal function and the incidence of glomerulosclerosis in spontaneously hypertensive Fawn Hooded rats (FHR). DESIGN: Male FHR were treated with captopril from the age of 5 months when mild hypertension, proteinuria and glomerulosclerosis are present, and sacrificed at 12 months of age. Renal function was determined in separate groups of FHR at 6 months of age. METHODS: Proteinuria, body weight and systolic blood pressure were determined at regular intervals. Blood pressure was measured by the tail-cuff method. Kidneys were prepared for histological examination by standard methods. Renal function was determined by inulin clearance and urinary kallikrein by an amydolitic assay. RESULTS: In untreated FHR blood pressure, proteinuria and glomerulosclerosis increased with time. Captopril normalized blood pressure and stabilized proteinuria at pretreatment levels. At the end of the study, the incidence of glomerulosclerosis was significantly lower and comparable with the incidence at 5 months. Glomerular volume did not show a correlation with the incidence of glomerulosclerosis. Hemodynamic studies showed a significant increase of glomerular filtration rate in captopril-treated rats. No statistically significant effect was seen on renal plasma flow or filtration fraction. Urinary excretion of kallikrein was increased in captopril-treated rats. CONCLUSIONS: CEI is effective in protecting the kidney from structural damage in hypertensive FHR even when treatment is started under conditions of established glomerular injury. The protection given by captopril is probably related to intrarenal effects.

Blood pressure control by the renin-angiotensin system in normotensive subjects. Assessment by angiotensin converting enzyme and renin inhibition.

BACKGROUND: The participation of the renin-angiotensin system in the control of blood pressure in normal, sodium-replete subjects is not clear. The use of a specific inhibitor of human renin should allow a better delineation of the importance of this system. METHODS AND RESULTS: Blood pressure responses were measured 1 hour after randomized, double-blind administration of the renin inhibitor Ro 42-5892 (600 mg p.o.) or the angiotensin converting enzyme inhibitor captopril (50 mg p.o.) in 20 healthy men on an ad libitum sodium diet. Effective inhibition of the renin-angiotensin system by either compound was indicated by increases of immunoreactive renin associated with an increase of angiotensin I production rate of 67.8 +/- 33.6% after captopril and a decrease of 79.5 +/- 16.4% after Ro 42-5892. Furthermore, Ro 42-5892 decreased plasma renin activity by 64%. Whereas intra-arterial diastolic (60 +/- 5.1 to 51.4 +/- 7.2 mm Hg, p less than 0.01) and mean arterial (77.7 +/- 6.0 to 71.4 +/- 8.5 mm Hg, p less than 0.001) pressures decreased after captopril, they remained unchanged after Ro 42-5892. Captopril, but not Ro 42-5892, increased forearm blood flow (2.4 +/- 0.8 versus 1.9 +/- 0.8 ml/min/100 ml, p less than 0.01) and significantly enhanced the increase of forearm blood flow to brachial artery infusions of bradykinin (0.15, 1.5, 5, 15, and 50 ng/min/100 ml; 5 minutes each) from 744 +/- 632% to 1,383 +/- 514% (p less than 0.01). Furthermore, repeat bradykinin infusions resulted in further decreases of blood pressure (from mean pressure of 71.4 +/- 8.5 to 63.2 +/- 7.6 mm Hg, p less than 0.01) only after captopril. Changes of blood pressure after captopril were unrelated to baseline plasma renin activity but correlated with captopril-induced enhancement of vasodilation to bradykinin (r = 0.68, p less than 0.05). CONCLUSIONS: The lack of blood pressure effects of renin inhibition in contrast to angiotensin converting enzyme inhibition suggests that the renin-angiotensin system does not contribute significantly to blood pressure control in normotensive, sodium-replete subjects. The hypotensive activity of angiotensin converting enzyme inhibitors may result from additional hormonal effects, for example, inhibition of bradykinin degradation and/or subsequent increases of vasodilating prostaglandins or endothelium-derived relaxing factor(s).

Influence of single- and multiple-dose omeprazole treatment on nifedipine pharmacokinetics and effects in healthy subjects.

The effects of single dose (20 mg) and short-term (20 mg/day for 8 days) oral treatment with omeprazole on the pharmacokinetics and effects of oral nifedipine (10 mg capsule) and on gastric pH have been investigated in a randomized, double-blind, placebo-controlled cross-over study in 10 non-smoking healthy male subjects. The single dose of omeprazole had no significant effect on any pharmacokinetic parameter of nifedipine, nor on gastric pH, or blood pressure or heart rate. Short-term omeprazole treatment increased the AUC of nifedipine by 26% (95% confidence interval 9-46%), but all other pharmacokinetic parameters of nifedipine, including elimination half-life, Cmax, tmax, and recovery of the main urinary metabolite, were not significantly changed. The median gastric pH during the absorption phase of nifedipine was increased by short-term omeprazole (pH 4.2) compared to placebo treatment (pH 1.4). Blood pressure and heart rate did not differ between treatments. The interaction between nifedipine and omeprazole is not likely to be of major clinical relevance.

Effect of the renin response during renin inhibition: oral Ro 42-5892 in normal humans.

The effect of the new renin inhibitor Ro 42-5892 was evaluated in healthy volunteers after both intravenous and oral administration. In a preliminary study, 14 subjects received a 10-min infusion of Ro 42-5892 at doses ranging from 0.001 to 1 mg/kg. Plasma renin activity (PRA) and angiotensin (Ang) II levels were maximally suppressed in a dose-dependent manner at the end of the infusion. Plasma active renin concentration increased up to threefold. In a second study, 24 volunteers received placebo or 100, 600, or 1,200 mg of Ro 42-5892 p.o. in a single-blind, randomized fashion. Within 30 min after drug intake, PRA and plasma Ang I and Ang II levels fell to their nadir. Both Ang I and Ang II were measured specifically after extraction on phenylsilylsilica and separation by isocratic HPLC. The degree as well as the duration of inhibition were dose related. The decrease in plasma Ang lasted maximally for 2 h. Active renin increased dose dependently and remained elevated for more than 8 h after the 1,200 mg dose. A theoretical generation rate of Ang I was calculated for individual plasma samples assuming Michaelis-Menten kinetics for competitive inhibition and steady-state conditions. This calculated Ang I generation rate, based on plasma active renin concentrations and drug levels, closely correlated with actually measured Ang I and Ang II levels (r = 0.90, n = 88) over the whole 8 h time period. Thus, a sustained renin inhibition by Ro 42-5892, as indicated by increased plasma active renin levels, induces a much shorter fall in plasma Ang I and II apparently because of a rise in renin secretion.

Does regional norepinephrine spillover represent local sympathetic activity?

Regional spillover of norepinephrine (NE), based on isotope dilution and single-compartment steady-state kinetics, is considered one of the best parameters for estimating organ sympathetic activity. However, the effects of local changes in clearance of NE on the spillover have not yet been investigated. We studied local NE kinetics and clearance in the forearm of 10 healthy subjects using intra-arterial infusions of NE, tritiated NE, the neuronal uptake inhibitor desipramine, and tyramine, which competes with NE for the neuronal uptake carrier. Before and during complete blockade of neuronal uptake by desipramine the venous concentration-time curves for tritiated NE and for NE released by tyramine were biexponential, consistent with the presence of (at least) two compartments for circulating tritiated NE and for locally released NE. The time constants for tyramine-induced release of NE and, in the same subjects during desipramine infusion, for tritiated NE were almost equal at the same level of forearm blood flow. This argues against possible diffusion or transport differences for NE to and from the circulation and the synapse. The regional intrinsic clearance capacity (a measure of the maximal ability of an organ to irreversibly remove drug by all pathways in the absence of any flow limitations) for NE decreased in the forearm by 65% (p less than 0.01) during neuronal uptake blockade by desipramine; the forearm clearance decreased by 59% (p less than 0.001), whereas the spillover rate of NE increased from 33 +/- 5 to 63 +/- 11 pmol.min-1 (p less than 0.05). Nitroprusside-induced increments in blood flow increased the spillover of NE from 18 +/- 4 to 35 +/- 6 pmol.min-1 (p less than 0.01); the clearance of circulating NE also increased (by 58%, p less than 0.05), and the intrinsic clearance capacity remained unchanged. This demonstrates that regional spillover of NE is markedly influenced by local changes in clearance and flow. The new parameter plasma appearance rate of NE is proposed. Although also derived from isotope dilution, this parameter may better approximate the regional entry of NE into the blood pool than spillover. This is corroborated by the nonsignificant changes of plasma appearance rate of NE during our desipramine and nitroprusside infusions.

Nonparallel effects of renin inhibitor treatment on plasma renin activity and angiotensins I and II in hypertensive subjects. An assay-related artifact.

Nonparallel effects of renin inhibitor treatment on plasma renin activity (PRA) and the plasma levels of angiotensins (ANG), as well as on blood pressure, have been observed in subjects with hypertension. This study addresses the possibility that renin inhibitors may show a high degree of plasma protein binding in vivo and that displacement of protein-bound inhibitor during the assay of PRA in vitro may lead to overestimation of renin inhibition. Indeed, with the ultrafiltration technique it was found that 96% of the novel renin inhibitor Ro 42-5892, when added to EDTA plasma, was bound to protein. The angiotensinase inhibitors phenylmethylsulfonyl fluoride (PMSF) and 8-hydroxy-quinoline sulfate (8-OHQ), which are currently used in PRA assays, caused a displacement of protein-bound inhibitor, thereby increasing its free concentration. This displacement was sufficient to explain the reduction in IC 50 of Ro 42-5892, which was seen in the PRA assay when PMSF and 8-OHQ were added to plasma. Such reductions in IC 50 were also seen with the renin inhibitors CGP 29-287, CGP 38-560A, and SR 43-845. When Ro 42-5892 was given, 1 mg/kg intravenously in 10 min, to subjects with hypertension, it appeared that plasma ANG I and II returned to baseline after 6-8 h, whereas PRA measured in the presence of PMSF and 8-OHQ was still suppressed. However, when PRA was measured without these angiotensinase inhibitors, the inhibition of PRA was parallel to the suppression of ANG I and II.(ABSTRACT TRUNCATED AT 250 WORDS)

Diurnal variation of essential and physiological tremor.

Evaluations were made of the diurnal variations of tremor power at rest, after fatigue and after mass loading, and plasma norepinephrine in patients with familial essential tremor and normal subjects. Diurnal tremor power rhythms for both essential and physiological tremor pursued identical temporal profiles. Plasma norepinephrine levels followed a congruent diurnal pattern with later peak values than the peak values of tremor power. Sympathetic nervous system activity is unlikely to be the cause of diurnal tremor power variation. The consistent diurnal rhythm of tremor power may affect dosage schemes of tremorolytic drugs.